Process for oxidation of benzene to phenol promoted by added ethers



APril 20 1948- R. H. KRIEBLE Er AL 2,440,234 f PROCESS FOR OXIDATION OFBENZENE TO PHENOL PROMOTEDBY ADDED ETHERS Fiied June 5, 1945 4 ww @wwPatented Apr. I20, 1948 PROCESS FOR OXIDATION OF BENZENE TO PHENOLPROMOTED BY ADDED ETHmS Robert H. Krieble, Schenectady, N. Y., andWilliam I. Denton, Woodbury, N. J., assignors to Socony-Vacuum OilCompany, Incorporated, a corporation of New York Application June 5,1945, sei-isi No. 551,658

This invention has to do with the production of 8 Claims. (Cl.Zitti-621) phenol by the oxidation of benzene and is more particularlyconcerned with that typev of process wherein aureaction mixturecomprising benzene and oxygen or molecular oxygen-containing gas such asair is passed through a reaction zone void of solid `catalyst, underpressure and at elevated temperature.

'I'his application is a4 .continuation-impart of our copendingapplication Serial No. 565,928, illed November 30, 1944, which, in turn,is a continuation-in-part of our application Serial No. 395,016, iledMay 24, 1941, now abandoned.

We are 'aware of the fact that processes of this general character haveheretofore been proposed, and in this regard, reference is made to theBone et al. Patent No. 2,199,585 and the Moyer et al. Patent No.2,223,383. Each of these patents discloses a process of the generalcharacter above' referred to, and each mentions that the process thereindisclosed can be carried out by recycling. We have discovered, however,that although the process of Bone, forexample. if used with a relativelyimpure grade of commercial benzene, can be operated to obtain a. fairyield of phenol on a small number of passes in a recycling operation,the conversion to phenol rapidly decreases with successive cycles, thusmaterially restricting the scope of the process and rendering itimpractical as a recycle operation. We have also observed that if achemically pure (reagent grade) of benzene is subjected to the processof the Bone patent,

no substantial conversion to phenol is obtained.

Since the percentage conversion of benzene to phenol in anoxidationtprocess of the class described is relatively small, it isobviously essential 'from the standpoint of practicability that theoperation be one in which the unconverted benzene can be continuouslyrecycled with a substantially constant conversion and yield of phenolunder a given set of operating conditions. It is the primary object oithis invention to provide such a process.

Ethers typified by diethyl ether are phenol and other oxidationproducts. The ethers, which form the subject matter of this invention,may be aliphatic, aromatic, cyclic or terpenic, or their substitutedanalogs. Representative ethers l which have Ibeen found to be effectiveherein are diethyl ether, Chlorex (Ay-dichiaro ethyl ether), dioxane andascaridole.

This invention is predicated upon the discovery that a minor proportionof an ether added to benzene substantially improves the conversion to.and yield of, phenol from benzene under the conditions of reaction inthe process contemplated herein, over the conversion and yield obtainedwithout said ether. The present invention is also predicated upon therelated discovery that if a minor proportion of an ether is continuouslyin..

` troducecl into the stream of benzene entering the reaction mixture,the conversion to, and yield of, phenol from benzene is appreciablyincreased over the conversion and yield obtained without said zene andair, or other oxygen-containing gas, is

thoroughly mixed and pre-heated to the desired temperature and passedthrough a reactor tube which has beenpre-heated and which for thepurpose of pre-heating and dissipating the heat of the exothermicreaction is immersed in a suitable heat-transfer bath, such as salt. Thereaction mixture, as will hereinafter be explained, Ais preferablymaintained under pressure. With properly regulated conditions a part ofthe benzene is thus oxidized to phenol. This phenol and the gaseous andhigh-boiling products of oxidation are then separated from the benzene.which is subsequently recycled through the mixer-preheater and reactor,Additional air is of course added prior to the admission of the :benzeneto the pre-heater-mixer, and in a continuous operation makeup benzene isalso added to replace the benzene converted. K

In such an operation we have found that where a commercial grade ofbenzene, such'as 90% Benzol," is used as the charging stock and isrecycled through the reactor with no additions of make-11D view that themechanism 3 make-up the benzene converted, the reactivity and conversionto phenol is not markedly lncreased. However, in an operation of therecycle type just described, if a minor proportion oi' an ether,l suchas diethyl ether. is continuously added to the charge of benzene, asteady conversion performance may be obtained and the reactivity, asindicated by the per cent conversion and yield of phenol at a giventemperature, is greatly increased. We have found that the reactivity ina process of the class described under a given set of conditions may begreatly increased by the incorporation in the reaction mixture of aminor proportion of an ether.

As indicated above, no substantial conversion of a. chemically pure(reagent grade) benzene to phenol takes place in the processcontemplated herein. The results provided below in Table 1 serve toillustrate the improvement realized by the use of an ether in theoxidation of benzene to phenol. The single-pass runs were made with'reagent grade benzene in a stainless steel tube 15' long and 0.12"inside diameter, at 1000 pounds per square inch and at a reaction timeof about 35 seconds with the approximate mixture BCeHs-l-Oz-l-lNz Highboiling products obtained in the runs are designated as H. Bs." in thetable.

It is readily seen that small, and almost negligible, conversions ofbenzene to phenol areefiected when reagent grade benzene is used alone;and, where typical ethers are used, appreciable conversions areeffected. Although the conversions with' these preferred inductors areonly of the order of about 2%, such conversions may be maintained in thecontinuous operation by maintaining the proper Inductor concentration ineach pass.

Although we do not wish to be bound by any theory as to the mechanism ofthis reaction or the part whichth ether plays in increasing thereactivity and conversion to phenol, it is our as represented by thefollowing equations will explain most of the observed facts:

CQHIOH (b) Reaction I is slow and determines the rate. Reactions II andIII, since they involve radicals, should be extremely rapid. ReactionIII is shown as a competition of phenyl and hydroxyl radicals for phenyland is probably over simplified. The essential fact is that in thepresence of a material which can be more readily dehydrogenated by O2than benzene.- H0z is produced independently yof reaction I and at alower temperature. It is then capable oi' reacting rapidly with bell- 4zene by Reactions II and III to produce the usualproducts.'

Under these conditions, far more phenol survives, less diphenyl isformed, and the yield is greatly improved.

According tothe foregoing mechanism, then. an inductor or promoter foruse in a process of th'e type contemplated herein is any compound whichis a betterhydrogen donor than benzene under 4the conditions of thereaction'zone; or, stated in another way, a promoter or Inductor may bedenned as a compound containing hydrogen and possessing 'the propertiesof being in the gaseous phase under the conditions of the reaction zone,and under said conditions, reacting with oxygen to form water at a lowertemperature than the temperature at which benzene so reacts with oxygen.

'Of the ethers contemplated herein, diethyl ether and chlorex areparticularly preferred.

As stated hereinabove, the promoters contemplated by the presentinvention are better hydrogen donors than benzene under the conditionsof the' reaction zone. In other words, the promoters in our process arehydrogen-containing materials which release hydrogen more readily thanbenzene under the conditions of reaction. 'I'he rates of hydrogenrelease from numerous materials are available in the chemical literatureand may be resorted to in selecting effective promoting materials. Fromsuch data we have derived potential hydrogen donor ability (P. H. D.A.). values for various materials and have found those-materialshavingvalues above a certain wherein K is the speciic velocity constant;C is minimum are effective in our process. The P, H.

AD. A. value relationship thus provides a means whereby a chemistskilled in the art may readily determine, with a high degree ofcertainty. whether or not a material will be an eiective promoter. A

'I'he P. H.`D. A. values obtained for various materials are derived inthe following manner. Hydrogen atoms are classied here into fourcategories: primary, secondary, tertiary and hydrogens attached to anoleilnic bond or an aromatic ring. No attempt li'as been made toevaluate bonds other than the carbon-hydrogen bond. With this as astarting point and taking activation energy values from the chemicalliterature, it is possible to evaluate relative ratios of release of thedifferent hydrogen atoms from hydrogencontaining materials. Averageactivation energy values taken from 'I'he Aliph'atic Free Radicals (F.O. Rice and O. K. Rice,- Johns Hopkins Press;

1935) are as follows:

Aterge Difference in Type of Hydrogen Atom Enragon ActivationKilocalories Energy Oleilnlc (Aromatic) 103 0 Primary 97 6 Relativerates of hydrogen release under conditions typical of our process, as at427 C., are

calculated from the well known relationship:

E K=0e RT a constant; E represents activation energy (in calories); R isa constant (1.987 calories); and T is absolute temperature (in degreesKelvin). The relative rate of a primary hydrogen atom as vconstant valuehas 5 i Y compared with an oleiinie hydrogen atom is calculated asfollows:

am Kaw?" im. im)

log Kay-F4364 In this manner it ii found that the several hydrogen atomshave the following K values at -Olennlc (aromatic). 1

Secondary 215.

Tertiary 12st The foregoing Karo. values indicate that a primaryhydrogen atom is released 'I3 times faster than an oleflnic or aromatichydrogen atom. Simplifying this (0l value to an oleiinic or aromatichydrogen drogen atoms. Hydrogen atoms attached to carbon atoms which arein the alpha position -to an olennic bond or some electronegativ'e groupsuch at keto (C=O) ether (-0-) or ester ('-COOR) are released from themolecule at an increased rate. It is dimcultto evaluate this eiIectsince it depends largely upon the structure oi. the molecule. It isrecognized that diilerent substituent groups such as olefin, ketone.etc., groups may activate hydrogen atoms to different degrees. Forconvenience, however. a

been assigned to such activation. vAccordingly,'whenever a primaryhydrogen is in an activated position, it is assigned a value equivalentto a normal secondary hydrogen. Similarly, atom is assigned a valueequivalent to a normal tertiary hydrogen atom; and for an activatedtertiary hydrogen atom, the normal rate is doubled. The P. H. D. A. of acompound, on a weight basis. is the sum of all the evaluated hydrogenatoms multiplied by a factor of 'ten and divided by the molecular weightof the compound.

From the Km o. values of 0. 1, 3 and 15 shown above. the P. H. D. A.values of hydrogen-containing materials are easily calculated. By way ofillustration, diethyl ether has six primary and four activated secondary(alpha to an olefinv bond) hydrogen atoms: therefore, diethyl ether hasa P. H. D. A. value, on a weight basis of y 9.0

.process as promoters are in substantial agreelment with the'experimental results` obtained.

However. in the case of first members of the various chemical classeswhich often behave differently than all other members of their classes.

relationship by assigning a zero ester, ether,

an activated secondary hydrogen 6 somediscrepancies obtain between theRED. A. In general.

values, on a weight basis.' of are ineffective. and those greater thanabout 2.5 are effective: however. those having values greater than! aregenerally oharactcrld by a high degree of effectiveness. 'Ihisrelationship is shown in the following tabu- 10 lation:

l0 As will be readily apparent benzene and lnimma. 0mm t (weight) tetrall-ethyl. 8propyl wolein turpentias taken as pinene) ath lnnth diauliidethe art. the apparatus used in carrying out a lprocess of the typecontemplated herein may take various forms. In the accompanyingdrawings. however, we have shown diagrammatieally one form of apparatuswhich may be satisfactorily used in carrying out an operation for thecontinuous conversion of benzene to phenol. As will hereinafter appear,the conditions of operation embody a number of variables which may bechanged with respect to one another over relatively wide limits, and noattempt will be made in describing the apparatus to take account ofthese possible chanses in variables.

Referring now to the drawing, reference numerals IlV and il indicateconduits which carry are connected through suitable valves I2 and I2'with the inlet I3 of a pump Il. vThe pump Il delivers the benzenethrough a conduit li to a T-connection Ii, where it is introduced into amixing conduit i1 leading to the coils I U of a mixer and pre-heatermounted in an insulated case I! which is lled with a suitableheat-exchange medium such as Dowthermf Reference numeral pressor whichdischarges into pipe 2| connected through the connection 22 to acompressed-air storage reservoir 23. The pipe 2l discharges through apressure-reducing valve 24 and an orifice now-control 2B into theconduit I1through which the airand benzene-reaction mixture is conductedto the mixing and pre-heating coil il. The inductor or promoter isintroduced into the reaction mixture at any suitable point, preferablyin the benzene stream, through a conduit as indicated by nunerall 28,such conduit being provided with a metering valve 29 to control thequantity of an inductor. such as diethyl ether, which is introduced.

The pre-heating and mixing coll II, wherein the benzene-promoter-alrmixture is initimately mixed and pre-heated to a. temperature below 20indicates an air-comr trated. the liquid products transfer bath, such asa fused salt bath. capable of maintaining a close temperature control,such bath being contained in the insulated case 42, which is providedwith an inlet conduit 43 having a pump 44, the inlet 45 of whichconnects with a heat-exchanger 48 which can be used to raise thetemperature of the salt bath for initiating the reaction and, after theexothermic reaction y has started, can be used to dissipate the heat ofreaction and maintain a constant temperature. The heat exchanger 46receives the heat-cxchange medium from the tank 42 through a dischargeconduit 41.

In the form of the apparatus shownvin the drawing. the reactor tubes areillustrated as being U`shaped. and the discharge portion 4I' of therespective reactor tubes connect with a header conduit 50 whichdischarges into the coil 5 I of a heat-exchanger 52. For the thermalbalance of the process this heat-exchanger 52 is shown as beingconnected through conduits 53 and 54 with the mixer and pre-heater I9 sothat the heat-exchange medium is circulated by means of pump 55 from thebottom of the mixer and preheater. I9 to the bottom of theheat-exchanger 52 and back to the mixer and pre-heater through the pipe53. y

The cooled reaction mixture containing the phenol and other products ofthe reaction discharges from the heat-exchanger 52 through pipe 56-58'and filter 51 into a high-pressure mist-breaking tower 58 having ahigh-pressure gas-discharge valve 59 which may lead to a turbine.Discharge valve 59 is controlled by orifice ow-control 25 to maintain aconstant flow of air in pipe I 1. The liquid product accumulating in thebottom of the high-pressure tower 58 is conducted through apressure-reducing valve 60 into a lowpressure-packed tower 6I provided62 to release gaseous prod- This liquid product, which is a mixture ofphenol, benzene and hig -bilers," is delivered to the benzene-recoverystill 62; In the still, as illuspass through a preheater 63 and aredischarged through the discharge pipe 63' intothe bottom of thestill 62,where the benzene is distilled oil' by a steam coil reboiler 64. Thestill 62 is shown as being equipped With bubble plates 65 and a watercoil reflux-condenser 85'.V` The benzene vapors are discharged throughconduit 58 into a benzene condenser 66', from which the liquid productdischarged through conduit 61 is pumped by means zene conduit Il'.

The bottom of the benzene-recovery still `62 is provided with adischarge conduit 1 0 through which the mixture of phenol andhigh-boilers is pumped into a vacuum still 1I. wherein the phenol isdistilled oil by means of the steam reboiler coil 12 into thephenol-discharge conduit pump 8|. l been previously pointed out, theprocess contemplated herein embodies a number of as to the effect ofthese variables, each of them will now be discussed individually.

'I'he proportion of air that can be used t Preferred operating actortubes, for example, include a benzene to oxygen ratio of from 2.5:1 to8:1, and particularly a ratio of 4:1. In terms of air then, the mostpreferred ratio is 4CaHa:1Oz:4N2.

Reaction time value, there is a high-boilers and a corresponding declinein As preferred, the reaction time should fall within the range of 2seconds to about 100 seconds.

The optimum reaction time is about 8.5 seconds under the followingpreferred operating conditions:

charge Benzene havihg added thereto about 1% (by volume) of diethylether.

Reactor 0.36 inch internal diameter v stainless steel tube 60 feet long.l

MlXture 4CsH-f--l-4Nz Pressure 750pounds per square inch. Temperature---'175 F.

Pressure We have vobtained phenol in good conversion perature, otherconditions'being the same. Thus,

pounds per square-inch temperatures of the order of 1200 F. arerequired, at 2000 pounds pressure good 'results have been obtained at675 F. Since ferrous metal surfaces strongly catalyze total combustionat temperatures above 1000 F., it is" necessary to use inert surfacessuch as glass, enamel, silica. etc..

conditions with 0.36 inch4 in the reactor when operating at lowpressures and the concomitant high temperatures. In this connection,good results have been obtained in nickel tubes at a pressure of 350pounds per square inch where the optimum reaction temperature was about1030* F., and probably still lower pressures and higher temperaturescould have been successfully used. With iron tubes, sufficient pressureto keep the reaction temperature below 1000 F. is required, usually atleast 50o-1000 pounds per square inch. However, at 1000 poundspressure,- the use of nickel tubes instead of iron or stainless steeltubes presents no advantage.

The use of high pressure has certain fundamental advantages, however. Atlow pressures, even though a glass-lined reactor be used, the loss tooxides of carbon is materially higher than at high pressures instainless steel equipment. Furthermore, the minimum critical reactiontime` apparently increases with decreasing pressure; and, since for aconstant reaction time the rate of feed varies directly with thepressure (by deflnition), the maximum permissible rate of throughputfalls oil! very rapidly with decreasing pIBSSule.

There is also an upper useful limit of pressure. As the pressure israised, the temperature required to initiate reaction decreases, asexplained above. Furthermore, the boiling point of benzene is raiseduntil the critical temperature of liquid benzene (550 F.) is reached.where it remains unchanged as the pressure is further increased. Sinceitis advantageous to mix thoroughly the benzene vapor and air beforeinitiating reaction, in order that local regions of undesirably highoxygen-concentration be eliminated. it is not desirable to indenitelylower the reaction temperature by the use of extremely high pressures.There is a relationship between the maximum useful pressure and theinternal diameter of the reactor tube, since we found that the smallerthe internal diameter of the reactor tube, the higher the temperaturenecessary to initiate reaction. In a 0.36 inch internal diameter reactortube, 1500 pounds per square inch appears to'be about the upper usefullimit, `and we prefer a pressure of about '150 pounds per square inch.In general', however. pressures within the range of about 350 pounds toabout 1500 pounds per square inch serve the purposes of this invention.

` Temperature T-heV optimum reaction temperature can be varied from 600F. to 950 F. by changing the operating conditions, among the mosteffective of which are pressure, promoter concentration and internaldiameter of the reaction tube. As indicated above in the discussion ofreaction time. a temperature of about 775 F., is particularly preferredunder certain well-defined conditions.

Reactor tube enamel, glazed porcelain. or silica, is imperative. Atmoderate pressures (several hundred pounds per square inch), nickel issatisfactory. At pressures in the neighborhood of 1000 pounds per vsquare inch, low-carbon steel and stainless 'steel are satisfactory, andnickel prei' its no advantage.

As to the internal diametr if the reactor tube (4l-4V) successfuloperation has been obtained in tubes varying from 0.086 inch to 0.875inch in internal diameter. For iron tubes, the smaller the internaldiameter the higher the required pressure. We prefer to use a tubehaving an internal diameter in the neighborhood of 0.36 inch and tooperate with pressures in the range of from 350 to 1500 pounds persquare inch. Smaller tubes are equally satisfactory, but they requirehigher operating pressures. For a tube having an internal diameter of01.086 inch, pressures of from 2000 pounds to 3000 pounds per squareinch are recommended. Y

. The length of the reactor tube (4i-4 i apparently determines the rateof throughput, and the existence of a critical minimum reaction time fora tube of fixed length and internal diameter has already been discussed.Satisfactory results in the operation of a process of the classdescribed have been obtained with tube lengths of feet. and' tubes of atleast this length are recommended.

Mier-pre-heater tube As to the mixer-pre-heater tube (i8) any materialhaving suitable mechanicaly properties such as stainless steel issatisfactory.` The internal diameter of this tube should be sufficientlysmall to prevent reaction taking place therein, and the tube should besumciently long to provide the heating surface necessary for aheat-exchange that will maintain the-feed temperature within F. to 50 E.of the temperature of the preheater bath. The temperature of thepre-heater bath should be such that the reaction mixture discharged fromthe pre-heater coil i8 is at a temperature of about -150" F. below thetemperature maintained in the reactor bath in the case 42.

Inductor The required properties oi the inductors and the theory oftheir action. together with certain preferences therein to diethyl etherand chlorex and the like,y having already been discussed.

The concentration of the inductor may be varied depending upon thecharacter of the make-upstock, the conditions of operations, etc. Withdiethyl ether. which is a preferred inductor, we have found that thisconcentration should be maintained in the neighborhood of from about 0.2per cent to about 3.0 per cent, by volume, based upon the quantity ofbenzene in the fresh i'eed. We prefer, however, to use a concentrationof 0.5 per cent to about 1.5 per cent, by volume, in the total feed. andhave found that increasing the concentration of the inductor greatlylowers the optimum reaction temperature.

It will be seen from the foregoing discussion that a process of the typecontemplated herein vis susceptible of numerous operating conditionsthrough manipulation of the variables discussed;

and the present invention is not concerned with any particular set ofoperating conditions, but as aforesaid, is predicated upon the discoverythat greatly improved results and a continuous recycling operation maybe obtained by introducing surfaces of `the reactor tubes, such asglass, into the reaction mixture an inductor or promoiing compound ofthe type hereinabove discussed. It is to be understood, therefore, thatalthough we have described and illustrated a specific form of apparatusand have discussed in considerable detail various reaction conditionswhich may be employed in the operation of such apparatus, the inventionis not limited to this apparatus or to any particular set of operatingconditions, but includes within its scope such changes and modificationsas fairly come within the spirit of the appended claims.

We claim:

l. In a method for the continuous manufacture of phenol from benzenewherein a reaction mixture ofbenzene vapor and oxygen-containing gas ispassed under pressure through a reaction zone void of solid catalyst andmaintained at a temperature of between about 600 F. and about 950 F., toconvert a part of the benzene to phenol and other oxidation products,and wherein unconverted benzene is separated from the phenolv and otheroxidation products and is returned for recycling in the reactionmixture; the improvement which comprises: continuously incorporating inthe benzene so rezone, a minor proportion, from about 0.2 per cent toabout 3.0 per cent by volume, of diethyl ether.

2. In a method for the continuous manufac- .25 cycled, prior to itsadmission to the reaction" ture of phenol from benzene wherein areaction mixture of benzene vapor and oxygen-containiing gas is passedunder pressure through a reaction zone void of solid catalyst andmaintained at a temperature of between about 600 F. and about 950 F., toconvert a. part of the benzene to phenol and other oxidation products,and whereinunconverted benzene is separated from the phenol and otheroxidation products and is returned for recycling" in the reactionmixture;

the improvement which comprises: continuously incorporating in thebenzene so recycled, prior to its admission to the reaction zone, aminor proportion, from about 0.2 per cent to about 3.0 per cent byvolume, of dioxane.

3. In a method for the continuous manufacture of phenol from benzenewherein a reaction mixture of benzene vapor and oxygen-containing gas ispassed under pressure through a reaction zone void of solid catalyst andmaintained at4 a temperature of between about 600 F. and about 950 F.,to convert a part of the benzene to phenol and other oxidation products,and wherein unconverted benzene is separated from the phenol and otheroxidation products and is returned for recycling in the reactionmixture;

the improvement which comprises: continuously incorporating in thebenzene so recycled, prior to its admission to the reaction zone, aminor proportion, from about 0.2 per cent to about 3.0 per cent byvolume, of beta, beta'dichloro diethyl ether.

4. In the method of making phenol `wherein ether, beta, betr-ammorediethyl ether, and di` oxane, in an amount falling within the range offrom about 0.2 per cent to about 3.0 per cent by volume based on thequantity of benzene in said reaction mixture.

5. In a method for the continuous manufacture of phenol from benzenewherein a reaction mixture of benzene vapor and oxygen-containing gas ispassed under pressure through a reaction zone void of solid catalyst andmaintained at an elevated temperature to convert a part of the benzeneto phenol and other oxidation products, and wherein unconverted benzeneis separated from the phenol and other oxidation products and isreturned for recycling in the reaction mixture; the improvement whichcomprises continuously incorporating in the benzene so recycled, priorto its admission to the reaction zone, an ether selected from the groupconsisting of diethyl ether, beta, betadichloro diethyl ether, anddioxane, in an amount falling within the range of from about 0.2 percent to about 3.0 per cent by volume.

6. In the method of making phenol wherein a reaction mixture of benzenevapor and oxygencontaining gas is passed under pressure through areaction zone void of solid catalyst and maintained at a temperature ofbetween about 600 F. and about 950 F.; y the step of incorporating insaid reaction mixture diethyl ether in an amount falling within therange lof from'about 0.2 per cent to about 3.0 per cent'by volume basedon the quantity of benzene in said reaction mixture.

7. In the methodfof making phenol wherein a reaction mixture of benzenevapor and oxygencontaining gas is passed under pressure through areaction zone void of solid catalyst and maintained at a temperature ofbetween about 600 F. and about 950 F.; the step of incorporating in saidreaction mixture beta, beta'-dichloro diethyl ether in an amount fallingwithin the range of from about 0.2 per cent to about 3.0 per cent byvolume based on the quantity of benzene in said reaction mixture.

8. In the method of making phenol wherein a reaction mixture4 of benzenevapor and oxygen-l containing gas is passed under pressure through `areaction zone void of solid catalyst and main-

